In the conventional image encoding methods (for example, see Non-patent Literature 1) represented by the ITU-T standards denoted as H.26x and the ISO/IEC standards denoted as MPEG-x, it is possible to divide a picture corresponding to an image signal into units called slices and encode the whole picture on a slice-by-slice basis according to a raster scan order on the whole picture.
The HEVC standard (for example, see Non-patent Literature 2) that has been standardized as a new standard introduces a tile format which makes it possible to divide a picture corresponding to an image signal into tiles having a rectangular shape, and perform a raster scan within each of the tiles resulting from the division. This tile format allows division of the picture in the vertical direction, and thus can reduce the capacity of a memory for pixel lines.
For example, FIG. 1 shows an example where a picture is divided also in the vertical direction into tiles enclosed by solid lines. The areas enclosed by broken lines are sub-areas further divided as slices from the tiles in the middle of a raster scan. FIG. 1 shows a pattern in which each of the tile boundaries is not across any slice boundary, and FIG. 2 shows a pattern in which each of the slice boundaries is not across any tile boundary.